It has long been known in gas turbines to provide a dilution air zone in the combustor immediately downstream of the flame zone. The dilution air zone is conventionally located directly within the combustion annulus downstream of the fuel injectors but well upstream of the outlet of the combustor. Generally speaking, dilution air is injected into the combustion annulus for the purpose of controlling the temperature of hot gases.
With such arrangements, upstream of the dilution air zone both fuel and air are injected and ignited in the combustion annulus. It is also conventional for there to be a cooling air film introduced along the walls of the combustion annulus upstream of the dilution air zone. Of course, the hot gases that result from combustion of fuel and air then pass on toward the turbine blades.
As is known, it is important to be able to control the temperature of the hot gases as they enter the nozzle on their way to the turbine blades. This has conventionally been handled by injecting the dilution air into the hot gases in an effort to ensure thorough mixing and cooling prior to entry into the nozzle. While effective, this means of controlling the temperature of the hot gases is not entirely satisfactory in every respect.
More particularly, the need to provide the dilution air zone in the combustion annulus upstream of the outlet of the combustor tends to dictate the geometry. In other words, the length of the turbine is controlled to a significant degree by the necessity of having a distinct dilution air zone within a combustion annulus, i.e., there has been no available manner for satisfactorily shortening the length of the combustor, much less the diameter thereof, in order to reduce weight and expense. However, conventional designs have also failed to address still another serious problem recognized by those in this field.
In particular, the dilution air flow path is known to cool only a portion of the walls of the combustor. Thus, in a conventional annular combustor of a gas turbine, not only is it true that not all portions of the walls of the combustor are cooled by the dilution air, but the point of injection into the dilution air zone has rendered it impossible to effect any significant cooling of the turbine shroud or shrouds and, thus, of the nozzle and turbine blades. As a result, it has remained to provide a low cost, simple, reliable means of turbine shroud cooling.
In addition, there has been a need for a simple means of positioning a combustor in generally concentric preselected axial relation to a housing without the need for a fixed attachment therebetween. It will be appreciated that such an arrangement would be desirable not only because of a reduction in expense in terms of parts and assembly but also because it would permit the overall diameter of the combustor and housing to be reduced thereby further reducing weight and expense without any adverse effect on the performance of the gas turbine engine. For this reason, it has remained to provide a suitable manner for satisfactorily reducing the diameter of the combustor and housing while at the same time providing automatic positioning therebetween.
Still additionally, it would be desirable to provide a plurality of fuel injectors in circumferentially spaced relation in the outer wall of a combustor. However, inasmuch as the space between the housing and the combustor must typically be used as an air flow path, there has been no suitable manner of directing fuel to such an arrangement of fuel injectors without unnecessarily impeding the flow of dilution air. As a result, it has remained to provide a low cost, simple, reliable means of fuel injection.
The present invention is directed to overcoming the above stated problems by providing a unique compact gas turbine engine characterized by automatic combustor positioning, turbine shroud cooling, and circumferential fuel injection. While the invention has been described in connection with a radial flow turbine, it should be appreciated that the invention could be utilized with any gas turbine construction.